No. Just use their id. The only time you would ever need their SteamID in a variable is if they leave the server and you still need their info.
Or, if you really want them then get the SteamID of everybody an client_authorized().
PHP Code:
new g_szSteamID[33][32]
// ...
get_user_authid(id, g_szAuthID[id], charsmax(g_szAuthID[]))
And, only save the id of the person so you can use the SteamID string as g_szSteamID[id_of_saved_user].
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