The problems you have heard about on the net have to do with people who came to the UK via the ROI and then in the future they want to apply for Indefinite Leave to Remain (spouses and workers can apply for ILR after 5 years). Because they entered through the Common Travel Area, they do not have a UK stamp in their passport and hence have no way to substantiate their start date in the UK for residency purposes. This leaves them in a state of limbo, which creates anxiety and thus you see internet lore about transiting through the ROI making problems.
Tourists have the same problem, but it's slightly different. Instead of 6 months leave to enter, they only get 90 days leave to enter. This has the effect of making them overstayers after they have been in the UK for more than 90 days. This is because they mistakenly think that when they enter the UK, their ROI visa "automatically converts" to a UK one (a false assumption). And in other cases, visitors who enter the UK through the ROI become illegal entrants (especially if they have a criminal history in the US/Canada or have been previously refused a visit visa).
You didn't say what type of visa you have so I have covered both cases, the tourist case being topical for this group. If you have questions about a spouse or work visa, please use the Expats site.
Per commentary, if you arrive from the ROI and try to get a British IO to stamp your passport, he/she will adamantly refuse. Also, in an earlier, more relaxed era people used boarding passes to substantiate their UK start date. It doesn't seem to work well in this era so people find that channel hopping is a better strategy (i.e., go to Calais and return).