Why would a regular user of rechargeable NiMH battery cells need a battery conditioner/analyzer? I try to explain two main reasons here, which are pairing and conditioning.
First reason is proper pairing. When connecting several cells in series (like most cameras/camera trays do), having similar actual capacities between the cells both keeps the batteries in better condition and gives overall longer run time for your electronics.
How it works is that when connected to series, the weakest cell gets consumed in faster pace than any other. The larger the difference, the faster the weak cell runs dry. If we think about extreme case of 1:2 difference in actual capacity (or internal resistance, to be more exact, but it follows the actual capacity well enough for practical purposes) between the best and worst cell, the weakest cell would be loaded twice as much as the strongest one. This results in the weakest cell, already having lower capacity, getting emptied at twice the speed, and the whole circuit dying when the weakest cell is done with.
So, by using bad pairings together, you reduce the total runtime of your device and the weakest unit also gets more load than others, thus making it even worse in relation to the others, so after next charge it gets even more load (in proportion) and gets consumed even faster than before and so on.
To prevent this kind of death spiral you need to measure the actual capacities every now and then and then pick cells that are close to each other on that account. How I do it myself is that I order the cells by the capacity, and when I need X units, I pick the X best ones. This way the load gets balanced, because the now-best cells get used more often and thus they get closer to the others in actual capacity. However, lost capacity is not all forever lost, which gets us to the next point: conditioning.
The usual way of measuring capacity is also conditioning at the same time. How it works is that instead of the normal fast charge (which is often the only supported method on cheaper chargers), the unit is charged at very low speed, then discharged at low speed, and recharged again. During the discharge we measure the amount of power used giving as the actual current capacity.
The slow charge happens typically at 0.1C, meaning speed where it would take 10 hours to reach full capacity, and discharge at 0.2C, meaning the unit would go dry in 5 hours. C stands for nominal capacity of the unit, and number tells how large portion of that we try to load/unload in an hour. This kind of 0.1C/0.2C/0.1C cycle is also the IEC standard for determining battery capacity.
This kind of conditioning is recommended to be done something like once per 10 fast charges. Fast charging and not fully depleting (every) cell is typical for normal use, but both these leave some “memory” to the battery in question. Conditioning works to remove that memory before it sticks.
Many mid-range chargers have a separate function for fully discharging the cell before starting to recharge. This works as a rudimentary conditioning and it’s a lot better to use it regularly than to not use any conditioning.