Many FPL managers seem to take the view that the Bench doesn't matter, and - especially early in the season, when they're struggling to make their budget stretch - they may fill it up with super-cheap players who are virtually worthless, Indeed, they may even omit to transfer out players who are dropped or pick up long-term injuries, leaving a bench seat completely empty.
That is a very foolhardy approach to the game.
Here's why your Bench is so important:
1) It's useful to be able to rotate your back-up goalkeeper with your primary pick, to avoid his tougher fixtures. (And it's useful to have guaranteed back-up, if your primary keeper unexpectaedly doesn't start one week!)
2) It's also useful to be able to rotate your defenders away from tougher opponents. (Since you're usually only starting 3 defenders, you can get away with having only 1 good back-up on the bench; but it's risky. More choice is more value, more points potential.)
3) It's useful to be able to drop any player to the bench for a week - and replace him with an at least half-decent altnerative - if they're facing a particularly unpromising fixture; or if they're likely to be rested after a tough European game, or are facing a short-term absence for a minor injury or a ban. Sometimes, indeed, you might want to try to 'carry' a top player on your bench for a slightly longer period (an expected injury absence of a few weeks, or participation in a mid-season international tournament); you're often kind of locked-in to your best players, because they've increased in value so much while you've owned them that you might take a heavy hit from 'transfer tax' if you tried a short-term sell-and-buy-back.
4) You never know when you may need an 'automatic substitution' to get you out of trouble. Very, very often a top player will go missing right on the eve of the Gameweek, or even during the Gameweek, because of a training injury, illness, family crisis, car crash, spat with his manager, or whatever - and you have no time to adjust. That can happen at any stage of the season, even in the very first gameweek! You need to have decent players on your bench to fill in for any unexpected absences like that. Most seasons, I find I'm drawing on at least one auto-sub every 2 or 3 gameweeks; and needing 2 or 3 in one week is far from unknown! During the winter months, when injuries and rest rotations become even more common, you often need auto-subs every single week.
5) A strong Bench gives you much more flexibility to negotiate the occasional fixture speed-bump of a Blank Gameweek without needing to resort to paid transfers. (For example, if 5 of your players are involved in the FA Cup Semi-Finals, but you have 3 good back-ups on the bench you can replace some of them with, you only need to use 2 transfers to assemble a full starting 11. If you have any 'holes' on your Bench, your problem in that gameweek is much worse.)
6) It's good to be continuously 'set up' for the possibility of an opportunistic Bench Boost. It's difficult to get the most out of that chip, and really quite fatuous to try to plan for it too far in advance. Yes, it's nice to have everybody (all 15 squad members!) facing a really favourable fixture, but it's even more important to have all 15 of them fully fit and looking certain to start - that's not something that happens very often, and not something you can plan for more than a few hours ahead of the weekly deadline! Also, relative fixture difficulty can shift very suddenly and unexpectedly, as the form a leading team may crash while a struggling club rediscovers a dangerous bite; and hence a gameweek of fixtures that looked promising early the season may cease to be so, but while another gameweek comes to look much more attractive - at short notice.
Moreover, if you're hoping to coast by with a shit Bench for most of the season, you have to go to a lot of extra trouble to assemble a quartet of decent starters when you do want to play your Bench Boost.
It takes only a little bit of extra thought and care, and perhaps a paltry extra 1 or 2 million pounds of your budget to recruit a solid Bench - rather than a pants one.
It is always absolutely WORTH IT - even for Gameweek 1!