Well what I mean is that if you have a choice of how to run the amp, either at say 4 ohms or 2 ohms, I'd choose 4 ohms.
That's not to say that I would go with 4 ohms and sacrifice the power I would have gotten at 2 ohms. I would just get an amp to start with that would deliver that same power at a 4 ohm load instead of a smaller amp that can only deliver that power when you drop it down to 2 ohms, and only half that power at 4 ohms.
I don't like pushing my equipment to the very brink of what it can take before giving out. It's like you don't drive your car with the tach always redlining. Yeah the tach says the engine can run up to 7000 RPM's, but you drive at about 2-3000 most of the time. If you drove it with the engine wound up like a rubber band then it would give out in no time with worn out bearings and maybe throw a rod too. Instead, we drive more easily and the engine(with luck) will get you to 100,000 miles before the first tuneup is due.
That's how I feel about my amps and subs. I know they've got more to give, but I don't ask for it cause I chose an amp that would do what I wanted without having to try so hard.
I once heard someone say electronic devices hate heat. If you run the amp at a 2 or 1 ohm load just because you can do it, then you have more heat than you would at a 4 ohm load. Excessive heat will wear it out faster.
However, if you are on a tight budget and cannot afford to get the larger amps that will perform at 4 ohms, then you can go with the smaller sized ones and wire to drop it down to 2 or 1 ohm to get the power that you want(so long as the amp says it can do it). And it might even last for years, but how long for sure, we don't know. Could even depend on where you live. If you live where it's always hot and the average temperature is in the 80-90 range, then the amp back there in your trunk is going to get a lot hotter and stay that way longer than it would if you lived up north and the temperature was in the 70's and for only about 6-8 months of the year. Can also depend on how long at a time you play it. If your like me and it can run for as much as 30 minutes nonstop EVERY TIME IT'S ON AND EVERY SINGLE DAY, and anywhere from 1-4 hours at a time at least twice a month on road trips, then I like having the knowledge that my amp isn't back there "takin' one for the team" so to speak. It has no trouble at all doing what I ask, no matter what the outside temperature, or no matter how long it's on, and I know it will keep on doing that cause it's been doing it for 3 years straight. I'd say I put about 40 hours a month on my stereo. It gets played on average for more than an hour a day, cumulatively that is.
That may not even be a lot of time for some people. I just feel that I listen to it more than average and I want it to last a little longer than average. Many only listen to the stereo on their way to and from work. 15-20 minutes one way. Less than an hour a day. There have been times that I have played with my stereo for a solid hour AFTER I got home from work, not even counting the drive home. Or I get in and go driving around for 2 hours just listening and driving. I do this a lot. I can cycle through 2-3 whole CD's in that time. If my amp was back there running red hot, I feel it would have given out long before now.
Sorry I ran on so long. I wanted to be understood but not confuse you into thinking that it will not last long if you wire for lower ohm loads. Just that it can possibly last "longer" if it's wired concervingly. It's just something to think about.