Most transport type aircraft (as opposed to fighter or bomber type aircraft) have an Operating Data Manual with a specific target speed for a given FL and ISA deviation. You climb at the recommended power settings or IAS or whatever (as specified by the ODM) until your planned route FL. You are taught by your primary flying instructor as a basic flying technique to anticipate the level off, so these lessons continue in later life and you reduce the power and start the forward movement of the stick shortly before the levelling altitude (usually only about 50 - 100 feet before, depending on the climb rate of the aircraft). and so you arrive, with the altitude absolutely hacked, but still at the climb IAS, not the route IAS.
Once levelled, you now wait for the engines (at the cruise power setting) to do their job. Sooner or later, they do. Eventually, because you are level, not climbing, the speed increases and you arrive at the target speed.
But all of this takes time. Some people believe that if you climb to a couple of hundred feet above the cruise altitude, still at the climb IAS/power settings or whatever, and then convert the excess altitude into speed by diving, you will arrive at the target IAS a bit more quickly, which means that you can then settle down into the cruise a bit earlier.
For me, the jury is still out on this one. Looking at it theoretically, it seems to me that it is a transfer between kinetic energy (speed and engine power) and potential energy (altitude). As energy can be neither created nor destroyed, it shouldn't make any difference which way you do it. However, practically, whenever I've done it, it always does actually seem to me to appear to be working, and you do seem to arrive at the target cruise IAS a bit more quickly if you do climb above the target altitude and then descend to pick up the target speed. I'm sure it can't be true, but it just always seems that way when you're doing it.