The problem with not understanding tables and relying entirely on your computer is that you're pretty much screwed for subsequent dives if your computer dies during or just before a dive.
If you understand the tables and haven't gone into a deco obligation (according to the tables) on your first dive of the day, you can still run the tables and dive a second dive. If you don't know how to use the tables then you're stuck on the boat/shore while your buddies go diving.
This is not entirely true.
While the recommendation is to sit out - it is not required. If you're diving within recreational limits and the computer problem is simple battery replacement - then replace the battery and get back to diving. Just be smart about it.
The other option and the one that most experienced divers choose is to dive with redundancy - in this case two computers. You do not have to break the bank to own two computers. Perfectly good pre-owned computers are available all over the internet and in local shops selling used gear for under $200... in some cases much less.
Buy a primary you like and a cheap second so you can avoid any worries.