Generally speaking, many of the cases that I have handled over the last nearly 28 years involved searches of individuals. Many of the cases involving possession of marijuana or possession of drugs would certainly involve searches of individuals that were done without a warrant.
A police officer will usually procure a warrant if they wanted to search an apartment, a house or a dwelling where somebody resided, if they believed that there may be criminal activity going on. They will go to the prosecutor or the prosecutor will go to a judge with an affidavit, the judge will review the affidavit, talk to the police officer, swear in the police officer and then sign the warrant.
Most searches that are ordinarily done without a warrant usually happen when a police officer stumbles upon a situation, such as when they see someone is walking down the street with a bulge in their pocket that appeared to be a weapon, like a gun or a knife. The police would stop the person and they would be told to stand in a prone position so that the officer would be able to pat them down, which is usually when the officer would recover a weapon of some sort like a gun or a knife.
A warrantless search could also happen if an individual was walking down the street and the police officer either walked or drove by and saw them smoking what appeared to be a marijuana cigarette. The police officer may stop the person if they either saw it, smelled it or both, and they could arrest that individual, search them and perhaps find some contraband, such as marijuana or something else.
A search without a warrant would not necessarily be illegal, although in order to find that out the person would need to explain the circumstance to an attorney and the attorney would have to review the reports and speak to the prosecutor, to determine whether or not their challenge to the legality of that search would be fruitful and yield a positive result for their client.