Glad to see you learnt tables. I think some agencies now have the option of teaching EITHER a DC or tables at open water level, so some new students haven't actually learnt tables at all. I have come across divers who don't know or understand dive tables and just blindly rely on their computer, but I have also seen divers who have come up from a dive with a beeping dive computer and not understood what it meant ! I remember one conversation I had with an insta-buddy explaining them it was telling them they had ascended too fast and missed the 3 minute safety stop, to get the reply "it often does that, I wondered what it meant!"
So I would sum it up by saying the following -
1. No you don't NEED a dive computer, provided you understand dive planning with tables for the type of dive you are doing, plan the dive and dive the plan, and have suitable bottom timer and depth gauge.
2. A computer CAN make things easier, but only if you understand how it works and still carefully monitor it.
3. Because a computer uses a real world profile rather than an idealised square profile from a dive table you will normally get a longer dive before you reach NDL because it tracks you actual nitrogen exposure at your depth and time profile. (this is also why you should never rely on a buddies computer, they may have gone either deeper or shallower than your actual profile and their computer will reflect that).
4. Absolute best practice would be to plan your dive with a table so you know your NDL limits, plan a contingency (deeper or longer dive), then make the dive using the computer for the dive itself. That way if the computer fails you know you can still make a safe ascent (this is more relevant if you are doing a dive that may incur a slight deco obligation which you probably will not be doing yet).
5. Finally if you are diving tables and your buddy is diving a computer (or vice a versa) make sure you have discussed and agreed dive length, maximum depth and when you call the dive, make sure you agree, and stick to the agreement.
Safe diving and enjoy your first sea dives - Phil.