Well the point would be that you could change tyres if you wished. Now, some drivers would try to just keep going and some would work on the "splash and dash" principle towards the end of the race.
In effect you'd have an alternative strategy available unlike the current situation where you have to change tyres (i.e. it's a single strategy) and all you're doing is picking when. Perhaps the new Pirellis will give more stops which gives more chances to roll the dice but it's still just variations of one strategy.
I'd like two compounds and the driver can use one or both as they see fit. So a quick but "hard" driver might go long on the hard compound and then "splash and dash" the last 10 laps on the softs having trashed the hards. A "soft" driver might try to go the whole race on one set of harder tyres and hope that he can be consistently quick enough to prevent the "hard" driver making the required 25-30s required for his strategy.
The current "must use two compounds" rule is just there to economically justify the tyre company taking two compounds to the races. There is no racing need to have the rule.