It depends. I suggest you to look at the "Terms of Services" of each free provider.
For example Infinityfree seems to be truely free and the hosting specification look okay to start with. The worrying part is the CPU count which is limited:
1. CPU LIMITATIONS
In the computer you’re reading this on (regardless of whether that’s a PC, laptop, tablet, phone or something else), there is a processor. This processor, or CPU, does all the calculations for all the programs running on your computer. If these programs use too much processor power, your computer will slow down, possibly to the point of being unusable.
source: forum @t Infinityfree
So there is a limit but the weird part is that they keep it secret!
The exact amount of CPU power an account can use is secret. The reasons for this, as well as an analogy, can be found in the “How is the CPU usage calculated” section above.
source: forum @t Infinityfree
The analogy to the why is BS to my opinion because they do offer metrics in the premium version.
The challenge with above is that due this limitation you migh hit it very quick, restricting the amount of visitors you can receive on your website, which will have a massive impact on SEO and Google Adsense income. Imagine the Google crawler not being able to visit you website to determine ranking or loading a TTFB of > 5 seconds due to holiday season traffic. You can reduce hitting this limit by setting up a static website instead of a dynamic one like Wordpress CMS. I guess the free version quickly will show its bad side and will make you select the premium one (Nice sales funnel).
2. NO GUARANTEES
Section 26 of the TOS states they offer zero guarantees related to the performance of the free webhosting. That would make me worry! Big chance there are no backups and no engineers on standby when there is a network failure of performance is down due to a failing raid disk.