Secondary fermentation seems to have mixed reviews amongst experienced brewers. Those against secondary fermentation largely argue (1) there is an increased risk of contamination due to the transfer into the secondary, exposing the beer to the air and possibly an improperly sanitized fermenter, and (2) there are little to no benefits to be gained and much time to be lost by using a secondary - it doesn't significantly affect flavor (according to this camp), so bottle your beer sooner and skip it. Those in favor of secondary fermentation argue (1) beer sitting on trub for extended periods of time (more than 2-3 weeks) can gather off-flavors from the trub, and (2) secondary fermentation helps to clarify and condition the beer so that you obtain more complexity in the finished product.
I firmly sit the fence. I rarely use a secondary fermentation for ales, and I brew mostly ales. My rule of thumb is not to use a secondary unless there is the potential for some additional benefit. Here is my personal list of cases in which I find a secondary fermenter worth the extra effort:
1. High-Gravity Beers. I think "big beers" benefit from a secondary - anything equal to or above 1.072 OG. The primary reason that I believe big beers benefit is that there is simply more stuff in the finished product - both fermentables and unfermentables - and allowing the yeast to work its way through all that material can take time. I've found that the longer these beers have to meld flavors and aromas, the smoother and more complementary the finished product becomes. I could be mistaken.
2. Long Fermentation/Conditioning Beers. Beers that I intend to ferment for more than three weeks. For lagers, I think this is especially important. I just think 8-10 weeks sitting on trub might actually affect the taste. I am less convinced this is true for shorter periods (1-3 weeks). Over 3 weeks, I would get the beer off the trub. But this is just my "feeling" on the issue. If you are going to bottle condition your beers (or keg-condition them, or force-carb them) at room temperature, then the bottle/keg is a great place for secondary fermentation. If you are going to keg and force carb your beers in a refrigerated environment below 60 degrees, however, refrigeration will slow and sometimes stop conditioning - if this is how you carb your beers, a secondary fermenter should be used for anything conditioning for more than three weeks. Again, just my opinion.
3. Beers That Require Clarity. In the case of clarity, I use the primary fermenter until primary fermentation is done (the krausen drops), which is usually about a week. After that, I move it to a secondary for 2-3 weeks. Then I leave the beer in the secondary and cold-crash the beer at 35 degrees for 3-5 days. This results in a nice, clear beer - but the cold-crash will stop any conditioning of the beer with the yeast because the yeast will go dormant. If clarity is a seriously desired trait in the beer, additional clarity can be obtained by filtering the beer at 1 mc. The filter removes the yeast and proteins from the beer but doesn't affect flavor too much.
In your particular case, your beer isn't considered a "big beer" by my criteria, and your beer doesn't require any special level of clarity because it's a heavy Scottish Ale. Depending on your mash temperature, grain bill, and hop profile, you might have some additional taste/flavor benefits by letting the beer condition in the secondary, but this can just as easily be done in the bottle/keg at room temperature.
So I'd think that secondary fermentation is not necessary for this recipe.
I have not, however, brewed this particular recipe - so another poster might be able to help you with this specific beer.
