@gurerg, I affectionately call that method the “poor man’s link tracker”. I’ve done it myself, and it works if you are comfortable with developer code and coding html yourself. My domain host - HostGator - tracks traffic to my subdomains, so I am able to get a rough idea of number of visits to any custom LP I create. Maybe you are doing it this way, too?
If I’m not mistaken, however, the convenience and power of paying for link tracker software, such as ClickMeter or ClickMagick, is mostly two-fold:
MANAGE LARGE DATA IN ONE CENTRAL PLACE: when you are an affiliate who runs 10, 20, 50+ offers, each with a complex structure (youtube channel, blog, landing pages for each offer), the amount of data you need to manage starts to get out of hand. If you just started recently and only have one or two offers to manage, this is fine. It saves you $350 bucks a year.
GRAPHICALLY SEE YOUR KEY PERFORMANCE INDICATORS AT A GLANCE: The convenience of having a GUI (visual interface) and ability to just glance at a graph for 2 seconds and SEE which link is getting better CTR and conversions is the whole point of tracking. You want to see which campaign/link is your stallion and which is your pony so you can become efficient with your budget allocation and your effort/time. Also, with regards to campaign optimization, to understand the dollar value of each lead (super important number).
If you love number crunching, I guess you could build your own dashboard using Google sheets. I did, but I’ve got ClickMeter on my wish list very soon.