PROCEDURE some_procedure (
        some_parameter          varchar2        default null
    ) IS
    BEGIN
        IF some_parameter is null THEN
            --Run Code Block 1
        ELSE
            --Run Code Block 2
        END IF;
    END some_procedure;

 
    PROCEDURE some_procedure
    IS
    BEGIN
        --Run Code Block 1
    END some_procedure;

    PROCEDURE some_procedure (
        some_parameter          varchar2
    ) IS
    BEGIN
        --May need to check to make sure parameter is not null

        --Run Code Block 2
    END some_procedure;

I think either are useful.

For example, consider two valid usages of a proc

proc A(parm1,parm2,parm3);

proc A(parm1,parm2,parm3,parm4,parm5,parm6);

I'd overload them, because if I went down the 'default route, I then need to add code to ensure people dont call the proc with 4 or 5 parameters, because I want to limit it to only 3 or 6.

As for a "rule", my preference is similar to my logic above, in that, I try to come up with *usage* rules that make sense to the application. I'll explain with another example:

proc A(p1,p2) already exists. My intention is to change it to be proc A(p1,p2,p3). It still does the same basic function, its just been enhanced due to application requirements. I'd probably go with

proc A(p1,p2,p3 default null)

so that new apps can use the '3' parameters, and as yet unchanged apps can still call the old one. As they are upgraded, eventually the proc would just become: proc A(p1,p2,p3). I didnt overload because in reality I was still dealing with a single function...I just had a transient need due to the way I roll out application changes.

If I was building a radically changed function, that only some apps will use, then I'd probably go overload, ie proc A(p1,p1,p2,p4) because whilst the function ("A") is the same, the implementation is so different that it warrants a separate code base.

Finally..sometimes downtime imposes the need. I can add a new procedure to a package spec without invalidating any dependencies, so sometimes I'll go with an overload simply so I can roll out a fix online without no outage.

Hope this helps.