Dear Victor, All the peaks read from LC-MS is not always relevant. Before dead volume peaks from mobile phase background or something elute from column from previous injections. I hope it is useful to you.

Dear Victor, I assume from your question you are asking about mass peaks, and not chromatographic peaks? While not all peaks are relevant for both types of peaks (as mentioned by Hiten), the reason differs quite notably depending upon the peak which you are examining. I want to unpack Hiten's answer a little, assuming in all cases you are using ESI.

As Hiten noted, not all mass peaks are relevant, especially when running in full-scan mode. Often, peaks corresponding to plasticizers, column packing material, solvent adducts, previous injections etc. may be present in addition to the peak representing your analyte of interest. It is often good to have an idea about what to expect before starting - for example: do you expect to see a protonated or deprotonated ion? A sodiated or potassiated adduct? Calculate out the mass of your intended analyte, and then determine what the mass should be. If the observed mass deviates from the calculated mass, then reassess.

Similarly, mass peaks observable before the elution of the dead volume can be categorically disregarded.

Chromatographic peaks (often as a total Ion chromatogram or TIC) can similarly be disregarded where the mass spectra and retention times deviate from expected. Matrix may shift the retention time slightly, however, major shifts in retention or observed the mass (on MS instruments) or transition ratios/Qual/Quant ratios (MS/MS) will invalidate the peak, or hint at other issues in the LC/MS system.

I hope this helps, please feel free to ask any further questions.

You might want to review what constitutes a mass peak (scan level) as compared to a chromatographic peak (elution time level)  in LC/MS.

Method Mass Spectral Data Processing

Thank you so much @Hiten, Joshua and Luke.  I really do appreciate as your answers are of great help.  I will look at the perspectives you offered and get back to you if I run into any hitch.  

Usually peaks found in the placebo and solvents are deemed irrelevant since they are not the molecule(s) of interest.

@Victor, apologies for the late response. The responses you got should be helpful. If you're still struggling let me know.