If they pushed back hard you're likely to drop your 45 and move on to the next hand.
If they flat call then it's low straight for you and up/down draw for them.... could be very interestiing!
Even though you only had 45 preflop, nobody raised... you could possibly have given more thought to charging a limpers tax (I love that term) and if nothing else you're likely to find out who thinks they have a hand or not and this can help your decision making later on in the hand if you take it that far.
I see a LOT of NPL players that are more than happy to call the BB just to see a flop but as soon as anyone raises they shut up shop and fold and give you a dirty look for being so rude