Arithmetic operations on rasters with different spatial resolution

I’m going to apply arithmetic operators (especially difference, multiplication and division) on two bands belonging to two different products with different spatial resolution.
I will save results within the separate file in BEAM (.dim) format (not sure if this is the best format, I just try to store all data in one consistent format).

Am I allowed to do that or should I use Resampling tool to change their resolution firstly?
How will operators behave in case of NaN and zero values (especially in case of the division). Will this cause any errors? What about crop/subset operator? Should I also ensure that both products describe exactly the same area of study?

Within help I’ve found only following information
Bands in an expression always evaluate to scaled (calibrated) geo-physical sample value
which I’m not 100℅ sure how should I interpret.

If you want tow work with band arithmetic on bands from different products you should resample (if multi-size products) and collocate them before you do anything else.
Division by zero is handled in the Band Maths operator, if I remember correctly in such cases the provided no-data value is set. NaN is also considered. You can also explicitly check for NaN by using the function nan(@)

By default the scaled geo-physical values are used for computation if you reference a band. Not the raw counts. That’s what the sentence wants to say.

Could you please tell me what does “collocate them” means, please?
Which tools should I use?

Moreover, I encounter issues with Resample tool as described in following thread:

Raster > Geometric Tools > Collocation