My real-life FIDE rating is 1300-1400. The question is: To what extent should I memorise book moves for openings?

I have found it hard to memorise book moves, thus I play some more obscure lines, like the Ruy Lopez exchange, Snyder Sicilian as white and the Benko Gambit as black. The only more common opening I play is the caro-kann as white.

I think I'm okay with tactics. I've managed to hold my own against a 2100 rated player till the endgame where he better understood the nuances of the position and thus won.

How important is it for me to fully study the book to be better at chess?

I'm not a very strong player, but it seems like openings at the lower levels serve basically two purposes:

- Produce a time advantage in many positions. You don't always need to think as much during the opening if it's a theoretical position. This gives you more time to think once you get out of book. This is largely irrelevant in corr of any sort, though. It can be relevant in realtime chess, particularly blitz.

- Knowing what you will play vs the systems you see in practice gives you more experience in the sort of positions they produce, so your experience in these positions grows with every game. I'm sort of assuming you're going to stick with (for example) one system vs say the sicilian, and basically play it 100% of the time. If you play a c3 sicilian one week, and go for an open sicilian the next, and a closed sicilian the week after, then there's no advantage in this area.

The problem is, there are many things you can do to improve play. Relatively speaking, knowledge of specific openings at the lower levels is probably not the best bang for the buck, although I think everyone is guilty of it, to some degree anyways. Regardless, you should always look up the theory after the game so you don't make the same mistake in that opening again.