Just as an example:
Using air on PADI tables, doing a series of 60 ft dives for 33 minutes each (this is not an unusual gas usage), with a 1h surface interval between them, you can only do 3 dives in a day; the 4th attempt violates allowable bottom time. It is worse, if you go deeper or stay longer (i.e., better air consumption). 60 ft dives for 42 minutes; you can only do ONE dive in that sequence without either a longer surface interval, or a shallower or shorter repetitive dive. If the sequence is 80 ft for 21 minutes, you can only do the ONE dive without some kind of adjustment.
But with 32% Nitrox (the most common percentage), you can do the 60 ft for 33 minutes dives (with 1h surface interval) all day long, as many as you want, not just 3. Same with 60 ft for 42 minutes. No limit for the day. Same with 80 ft for 21 minutes.
The point is, Nitrox REALLY opens up repetitive diving. A computer MAY help, if the dive is multilevel (starts deep, works its way up shallower). But for a "square profile" (i.e., go down, stay, come up, which is typical of a lot of sites), the computer doesn't help nearly as much as Nitrox.