White Hot Spikes allows the Spike Factory to gain popping of any bloon type. While mostly used to allow Spike Storm and Carpet of Spikes to pop DDTs without additional support, White Hot Spikes is sometimes used to synergize better with Ice Monkeys or to pop up early Lead Bloons.
Generally speaking, the White Hot Spikes upgrade is perfect for Upper Path 2 upgrades, more specifically for the Spike Storm and Carpet of Spikes upgrades, in contrast to crosspathing those upgrades with Smart Spikes, which lacks potential for internal lead-popping.
While it helps MOAB SHREDR deal big damage to DDTs, most of the time other bloons will simply eat up the spikes, wasting potential versus DDTs. Its further upgrades, however, are the ones that benefit the most out of the White Hot Spikes upgrade.
This upgrade pairs well with Spike Storm, as it allows each spike storm ability to pop DDTs.
This upgrade also pairs well with Carpet of Spikes, as it allows the periodic spike storms and manual spike storms to pop DDTs.
It is recommended to get the first two upgrades of path 2 (Faster Production and Even Faster Production) before getting this upgrade, as producing spike piles at a faster rate is usually more valuable than allowing them to pop Lead Bloons.
The only exception is if going for Spiked Balls, where in this case it's usually better to just go straight towards 3-0-0 in most cases, unless a bit more bloon tanking is required before then. If that ever happens, purchase one attack speed upgrade, as it's cost-efficient to improve a Bigger Stacks Spike Factory.