There are two basic schools of thought with respect to card usage:
1. One deals with being as minimalistic as possible as they value time with regards to holding a number of cards (owing to not waste time in tracking cards and their respective spends, tracking card specific rewards, etc). Hence people usually keep less but premium cards which yield more value overall than the regular or co-branded ones so that they don’t have to get into calculation game every time they intend to or make a spend. They lose out on card specific merchant offers though.
2. Another section believes in maximizing the crap out of anything and everything related to credit cards and hence prefer to hold maximum of them to avail merchant offers across segments, hold more credit, get more chance of limit enhancement on existing cards, etc. They prefer LTF cards or the one which gives value to them (not necessarily in terms of rewards but might be non-spend based benefit as well) most of the time. This approach yields maximum returns but also asks to maximum time and effort to be devoted in order to get the maximum out of the spends made on such cards.
You need to decide your approach basis your comfort zone and acquire/utilise cards accordingly.
Here in TF community, almost everyone likes to collect cards... But deep inside we all know that we actually use only handful of cards and rest are just for the sake of being part of certain bank...
So, if I get the choice I would go with a minimalistic approach, i.e., 2-3 cards for all kind of expenses...
One for swipe purposes, one for everyday online payments and one for bigger monthly or once in a while payments